Usually they last the life of the shocks which can be the life of the car. If the boots on your Pedders shocks have failed then I'd go back to Pedders for comment as they should last the life of the shock. Be careful if you do decide to go back to them as they can be like used car salesmen and talk you into work you may not really want! To change you need to remove the spring struts, compress spring and disassemble..put new boot in and reassemble. May also need a wheel alignment.
Cheapest part unless you are doing it yourself would be the boot. I'd use generic boots - the ones that fit steering racks - cost under $20 a pair. If you paid for labour I'd hazard a guess at $400 both sides for a normal mechanic.
If you were real smart you may just be able to slit a boot lengthwise and slip it thru the coils when extended....that way it becomes pretty simple.
Good Luck.
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